I've read a few reports on Tweeters where birds have struck the windows of individuals who are evidently birders - at least Tweeters subscribers. There are so many relatively easy ways to avoid this.
Bird shops sell many kinds of unobtrusive decals that adhere either to the inside or outside of the window. Slightly more aesthetic, a long chain or string of colored beads or glass bits or shells hung at the top mid-window works well.
I have more window than wall, I feed birds and live in a rural area. By using the above treatments, I rarely have a bird strike.
Having worked in a bird rehab facility for years, let me tell you, most window strikes don't make it. They break either their necks or backs, or have such a severe concussion that they are unable to come back from it.
It's one small way we can protect the birds we enjoy so much.